The diets included a Step I Diet – a standard heart healthy diet with 25 percent fat and 8 percent saturated fat, a diet containing 1.5 ounces of pistachios that was a Step I Diet with 30 percent total fat and 8 percent saturated fat and a diet containing 3 ounces of pistachios that was a Step I Diet containing 34 percent fat and 8 percent saturated fat. At the end of each four-week diet regime, the researchers measured blood pressure and total peripheral vascular resistance at rest and during two stress tests.
The two tests consisted of a physical test and a psychological test. The physical test consists of putting one foot in a bucket of ice water for 2.5 minutes. The psychological test asks participants to listen to two numbers, add them in their head and say the answer. Then they hear another number and they must add it to the second number they heard, not the sum they spoke.
Note these results go against the simple rule that more fats are bad. Nuts are a more complicated story in part because their fats are less saturated.
Pistachios reduced the effects of stress on blood pressure. Stressful conditions did not increase blood pressure as much in people who were on diets that included pistachios. Pistachios caused artery relaxation.
The researchers found that both pistachio containing diets reduced the stress effects on blood pressure, but that the 1.5 ounce pistachio diet reduced systolic blood pressure by 4.8 millimeters of mercury while the 3-ounce pistachio diet only reduced systolic blood pressure by 2.4 millimeters of mercury. The diets had no effect on normal, resting blood pressure.
"When we only look at blood pressure, these results are confusing," says West. "If it is the pistachios, why is it not dose related?"
When the researchers looked at total peripheral vascular resistance, it was clear that the 3-ounce diet caused greater relaxation of arteries. Because the body tightly regulates blood pressure, rather than allowing blood pressure to drop further, the heart compensated by pumping more forcefully.
The artery benefits might come from the high concentrations of arginine found in pistachios and some other nuts. Pistachios have two and a half grams of arginine in a cup. The arginine helps boost nitric acid which relaxes arteries.
The multi-week study, which received funding from the California Pistachio Commission , concluded that three ounces of pistachios a day reduced LDL levels by 11.6 percent, total cholesterol levels by 8.4 percent, and non-high density lipoproteins (non-HDL) by 11.2 percent.
Lower cholesterol, less reaction to stress, lower blood pressure. Does the arginine story get any better? A different study by the University of Toronto’s Dr. Cyril Kendall and Dr. David Jenkins (he who developed his "ape diet" to lower cholesterol in humans) finds that pistachios reduce blood sugar rise after high carbohydrate meals.
Drs. Jenkins and Kendall and their research colleagues studied 10 healthy individuals who participated in a number of acute dietary studies over the course of two months. After an overnight fast, participants were given a one-, two- or three-ounce serving of pistachios alone or served with a slice of white bread and blood sugar levels were measured over a two-hour period. The findings suggest that consumption of pistachios with a carbohydrate-rich meal significantly lowered the d blood glucose response. As consumption of pistachios increased, the blood sugar lowering response was enhanced. In addition, when pistachios were consumed alone, the rise in blood glucose was minimal.
The researchers also monitored the effect of pistachios consumed with different common carbohydrate foods on postprandial glycemia, or blood sugar levels after eating. The addition of pistachios to a number of other commonly consumed carbohydrate-rich foods – such as mashed potatoes, pasta and rice – also resulted in significant reductions in the blood sugar response, compared to when these foods were eaten alone.
These results are consistent with a larger body of research showing health benefits from consumption of nuts. Curiously, pistachios have more carbohydrates than a lot of other nuts. Yet they provided blood sugar benefits.
|Share |||Randall Parker, 2007 May 01 09:16 PM Aging Diet Studies|